Quoting Jackbr (Thread starter):What are the general procedures for undertaking an emergency descent on an airliner?

Oxygen masks on
Establish communications with the other pilot

Start of loop

Select heading and commence a turn off the airway (as traffic maybe below)
Select a lower altitude and commence a descent (this should command the autothrust/throttle to IDLE)
Select the current speed/mach
Check speed, check autopilot/autothrust modes, check commanded thrust level
Select full speed brake whilst monitoring speed
Both thrust levers back to IDLE if the thrust is not at IDLE

The monitoring pilot sits on their hands and monitors these vital actions to ensure the PF gets the aircraft established in the emergency descent safely.

The PF repeats the first loop

Heading okay ? where is traffic/terrain ?
Altitude okay, what height is the terrain ?
Speed, was the aircraft damaged, if it was damaged (e.g. explosive loss of a cargo door) you would keep the indicated speed at the time of the explosive decompression, otherwise, select Vmo/Mmo
Check speed, check autopilot/autothrust modes, check commanded thrust level

The pilot monitoring at the same time as the PF make the second loop
Transmits a mayday call
Turns the engine igniters on
Emergency code on transponder
No smoking/seat belt signs on
Engine anti-ice if required
Lights on
Works through the electronic and/or QRH checklist

Nope, All airlines I worked at: Gear and flaps up! The speed needs to be reduced significantly to lower gear and flaps and then you cannot descent with Vmo anymore, you need to use Vle, or the max flap placard speed...
I think only about the 744 where flaps 1 to flaps 5 can take up to 30 seconds. In 30 seconds I have already descended 2000-2500 feet in clean configuration with speed brake extended and Mmo/ Vmo.

Quoting wilco737 (Reply 5):They can be used, but it has never been officially certified to use them above 20,000 feet, as there is no normal condition where you need it.

I would not use the word "can", if something is not permitted as it is an aircraft limit, it cannot normally be used.

It could only be used by the Captain if they had the view that the limit has be intentionally exceeded under their emergency authority for the safe outcome of the flight. Otherwise their licence could be revoked, or in worst case, end up in jail for wilful negligence.

We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar

I was on a flight a few years ago where we had an emergancy descent over Rotterdam, we were in a Gulf Air A330 going from DUB-BAH... There was a sudden jolt of turbulance that hit the aircraft, It seemed to take forever but in reality it was maybe only 10secs or less before the aircraft pitched down (you all mention throttles to idle but im certian the throttles were opened or power atleast significantly increased) a few moments later (about a minute) the captian came on and apologised for the sudden madness and advised we had hit some extremly strong turbulance and he had to commence an emergancy descent. We descended 7000ft as stated by the captain.
It was a thrilling ride to say the least but next time I think i'd like to know about it before it happens

Zeke has pretty much written everything to know on a modern airplane.
The only addition, may be, would be to consider a higher Mach /Ias for the descent if there is no structure damage.

Quoting zeke (Reply 4):Gear maybe used in the case of damage, as it will increase drag, normally gear and flap cannot be selected above FL200. Flap would not be used.

The use of the landing gear was a 741 / 2 / 3 SOP, the captain had a choice of whether use them or not. It allowed a slower IAS / Mach, limited to Vle .
The procedure was awkward as it involved all three flight deck personnel being rather busy. It was cancelled on the 744 on some airlines.

Quoting zeke (Reply 6):I would not use the word "can", if something is not permitted as it is an aircraft limit, it cannot normally be used.

Isn't that what I have written? I said, they can be used, but it has never been certified. Basically it is possible. Sure, it is a limitation which has to be observed under normal conditions... But what do I know...

Many newer bizjets have an Auto Emerg Descent feature. Autopilot and autothrottle commences an emergency descent without any pilot input when cabin altitude reaches +24;000' (?). The GLEX descends to and captures 15,000'. The system good if the pilots are incapacitated. I don't know if airliners have this feature.

No, your descent will be made on :
- idle thrust
- extended speed brakes
- high speed, selected
and all the above will make your descent, i.e your rate of descent, as high as can be.
- to the selected level-off altitude, which is in general FL 100 or MSA if higher.

Quoting wilco737 (Reply 18):FLCH is the one we use. Then the pitch will be adjusted automatically to maintain Mmo/ Vmo.

That's for the Boeings;
On the 'Bus, no need to select a mode, the procedures above automatically trigger the OPEN DESCent mode, equivalent to the Boeing FLCH on a descent profile.
I did not want to be type specific.

Quoting 26point2 (Reply 14):Many newer bizjets have an Auto Emerg Descent feature. Autopilot and autothrottle commences an emergency descent without any pilot input when cabin altitude reaches 24;000' (?). The GLEX descends to and captures 15,000'. The system good if the pilots are incapacitated. I don't know if airliners have this feature.

The L-1011-500 (and BA -200's) have a system called Recovery Speed Brakes (RSB). At high altitudes and high Mach numbers the Flight Controls Electronic System (FCES) computers reschedule the spoilers so all 12 spoiler panels are active, in lieu of just 10 active panels on aircraft without RSB. RSB allows the crew to fully deploy the spoilers (with the travel limited on some panels) and not worry about high speed buffeting that could be experience on those L-1011's not equipped with RSB's.

1.) Speed brake use during emergency descent - are they primarily used as spoilers (kill lift thereby increasing descent) or speed brakes (helping prevent the aircraft from overspeeding)? Obviously it will be a combination, but I'm just wondering which is the primary function in this case.

2.) What sort of deck angle will allow you to maintain Vmo/Mmo on idle thrust?

They can be used, but it has never been officially certified to use them above 20,000 feet, as there is no normal condition where you need it.

On some aircraft it cannot be used...the AFM limitation is actually coded into the flap actuation logic, so if you move the handle above 20,000' nothing happens.

Quoting ANITIX87 (Reply 11):What is the typical descent in FPM that one can achieve during an emergency descent? On a related note, what's the typical nose-down angle for maximum emergency descent?

You can get north of 15,000 FPM (briefly) on some more slippery designs during the initial pitch-over to capture speed. Once you catch up to the Mmo line, you can be over 10,000 FPM. Nose-down angle isn't as vigorous as you might think...maybe 15 degrees initially.

Quoting ANITIX87 (Reply 11):How much time elapses between the PF thinking, "We need to execute an emergency descent" to the moment when maximum descent rate is achieved?

A few seconds...the highest rate of descent is in the initial pitchover to accelerate to Mmo. Once you're on the Mmo/Vmo curve your rate of descent goes down.

Quoting vikkyvik (Reply 21):1.) Speed brake use during emergency descent - are they primarily used as spoilers (kill lift thereby increasing descent) or speed brakes (helping prevent the aircraft from overspeeding)? Obviously it will be a combination, but I'm just wondering which is the primary function in this case.

Primarily drag...the whole point of the exercise is to shed energy as quickly as possible.